1. Field of the Invention
The invention relates to a method for producing a metal sheet with a welded-on tube, which has at least partially curved sections, wherein the tube is guided by at least one guide element onto the sheet, is pressed thereon with at least one pressure element and is welded thereto at least at some points and wherein the tube is bent to form the curved sections.
Furthermore, the invention relates to a device for producing a metal sheet with a welded-on tube, which has at least partially curved sections, comprising at least one guide element, by which the tube can be guided and by which bending forces can be transferred to the tube, at least one pressure element, which is arranged adjoining the at least one guide element and presses the guided tube onto the metal sheet, and at least one welding device arranged at the side of the at least one pressure element, with which welding device, in a region of a contact line of the tube and the metal sheet, the tube can be welded on the metal sheet at least at some points under the at least one pressure element.
The above-mentioned metal sheets with welded-on tubes are generally used as heat exchangers, for example, as flat absorbers, typically in thermal solar collectors. With flat absorbers, heat is thereby transferred from the metal sheet heated by absorbed solar rays or an absorber plate to a welded-on tube and transferred from there to a liquid heat transfer medium located in the tube. For a high efficiency of the flat absorber or of heat exchangers in general, a good heat transfer is important, which depends at least in part on a quality of welded joints.
2. Discussion of Background Information
According to the prior art, methods are known for producing a metal sheet with a welded-on tube, wherein, e.g., a meandering tube is placed on a metal sheet and is welded thereto. In a first operation, the tube is bent into a desired shape, in a second operation a welding-on of the placed, pre-shaped tube on the metal sheet is carried out. In DE 10 2005 001 435 A1, a method of this type is described, which makes it possible to weld a tube curved in a meandering manner on the metal sheet even in curved sections of the tube. This method produces a good result per se, but today the trend with respect to the most efficient possible production method is towards removing the tube for welding on the metal sheet directly from a coil, without previously bending it into the desired shape in a separate operation. The method disclosed in DE 10 2005 001 435 A1 has the disadvantage that two separate operations to be performed consecutively are necessary for the bending and welding-on of the tube. In addition to a more complicated process sequence resulting therefrom which takes longer and takes up more space and is therefore inefficient, it is also disadvantageous that a continuous contact between the tube and the metal sheet cannot be achieved or can be achieved only with great difficulty.
From the prior art, as mentioned, methods are also known, wherein the tube is not arranged on the metal sheet pre-bent, but is continuously fed from a coil and bent. In a method of this type for producing a heat exchanger described in WO 2006/065195 A1, a tube is applied to a metal sheet from a coil by rolls and, in the case of a straight course of the tube, welded to the metal sheet in the same operation. In order to achieve a curved course of the tube, a welding is interrupted and the tube is bent into a desired shape by a pair of bending rolls. After the bending, the welding of the tube on the metal sheet is continued in a subsequent straight section of the tube. In the method described in WO 2006/065195 A1, although a number of the operations is reduced, the principle of the method means that a welding of the tube on the metal sheet during the bending or in the curved sections of the tube is not possible: a contact line between the tube and the metal sheet is covered by applied bending rolls in the curved sections and thus is not accessible for a welding device. The lack of welding points in the curved sections produces a poorer heat transfer between the metal sheet and the tube. Although the welding of the tube in the curved sections could be carried out in a separate, later operation, this in turn would lead to an inefficient method that would take a long time.